Hello guys,

I just bought a new longblock SBC 350 which was remanufactured.
It comes with vortec heads (10239906) and a mild performance cam (Elgin E921P). Besides that its a stock 1980 flat tapped Goodwrench block. (casting no.: 10066036)

My concerns are that the camshaft is a little too agressive and that it will cause too much reversion.

Here are the specs of the cam:

Advertised Exhaust Duration 288
Advertised Intake Duration 292
Basic Operating RPM Range 2000-4800
Cam Type Hydraulic Flat Tappet
Exhaust Centerline 114
Duration at .050 inch Lift 224
Exhaust Lobe Lift 0.307
Exhaust Valve Lift 0.460
Exhaust Valve Lift with Factory Rocker Arm Ratio .460
Intake Centerline 114
Intake Duration at .050 inch Lift 224
Intake Lobe Lift 0.300
Intake Valve Lift 0.450
Intake Valve Lift with Factory Rocker Arm Ratio .450
Lobe Separation 114
Intake Opens at .050 inch Lift -3 BTC
Exhaust Opens at .050 inch Lift 46 BBC
Intake Closes at .050 inch Lift 47 ABC
Exhaust Closes at .050 inch Lift -2 ATC
Over Lap 59.0

Which cam would you recommend? I want to be absolutely safe with the reversion topic.
I thought of the OEM cam (Mercruiser 431-5943) or a cam from CompCams, but I don't know wchich one is the mildest. Maybe the CL12-232-3?

I run the engine with cast iron center riser manifolds, a edelbrock 1409 with aluminum intake, so nothing wild.

Thank you for your advice!

Greetings Ben

Hi Ben,

I swapped the camshaft on my Mercruiser 350 MAG MPI from the stock one to a Comp Cams Xtreme Marine (PN 08-417-8, Duration 270/276, Lift .495/.503).
To install the new cam, I had to machine the cylinder heads to mount rocker arm studs (Comp Cams High Energy PN 4500-16), Beehive valve springs (PN 12499224), and matching retainers (PN 787-16).

Compared to the OEM Mercruiser cam, the torque curve shifted slightly toward the higher RPM range. Overall, the performance gain didn’t justify the effort and cost, so I’d recommend sticking with the OEM Mercruiser cam if you can find a good used one.

I actually have an OEM Mercruiser roller cam for the 350 available. I’m also located in the Stuttgart area — if you’re interested, I can make you an offer.
Greetings
Tobias

Hi Tobi,

nice to meet someone from my area here.

Yeah, thats what I thought. I just keep the stock cam specs I guess.

Do you know if the roller cam will work with my setup? The engine is a flat tapped engine, so I think I‘ll have to go for a linked roller lifter conversion.

I wanted to put vortec heads on also, so I absolutely don’t know if that will work out and which parts to use.

Where are you roaming around with your boat?

Greetings Ben

The Vortec Heads need guide boss cleanup if you increase lift much.

Vortecs will give you lots of easy power if you set them up well. The Flat Tappet cam can have more area under the curve if the Adv Duration is under 270. The FT lifter is not ramp rate limited like a roller lifter. ( a factor of lifter wheel diameter)

The problem is also with aftermarket FT lifters. They should be inspected to ensure you have a 0.0015" convex from center. Mark a line on the pushrods, and ensure they turn when cranking over after oil priming etc.

Quality aftermarket SBC link bar rollers are expensive. Starting out with a post '86 roller block helps reduce costs a lot for mild builds.

You won't be able to directly use the offered roller cam. It has a machined cut out to locate the cam with a cam retainer plate that mounts to the block. You would need a cam button retaining system. Not a fan of them...worse for a marine engine. An added failure point that can be avoided.

Unless you make an extra 50hp, you're not going to notice mich difference. A 260hp SBC to a 350hp SBC would really snap it up.

What was the long block advertised for HP?

Vortecs and take 0.470-0.480 lift max. Your 0.450" should be gtg.

114 LSA and 224° @ 0.050" isn't a big reversion risk...but coming up to it.

A 220/224 Vortec 350 crate engine comes out at 350/400 hp/tq. That's maybe a bit conservative. Depends on build etc.

Your exhaust may be the bottleneck. You get 115cfm per square inch of exhaust area. You need 2.2 cfm/hp for unrestricted (no back pressure) flow.

Hello Tartilla,

thank you for your information.

My status is now: Keep the Elgin E-921-P flat tapped cam and go for a head upgrade.

I ordered the following heads: 67cc vortec heads from summit (SUM-151124) with 175cc intake runner, they allow a max. valve lift of .490"
I will use the recommended valve springs with 104-116 lbs. seat and 273-297 lbs. open pressure. The camshaft states 100 on seat and 280 open.
Also I think the 114 Lobe will be fine with reversion (as the OEM cam has 112) and the 59 overlap is referred to 0.000" and not 0.050", so it will be around 20-25 on 0.050" I guess.

Those specs seem fine to me for a marine application, or what do you think?

I was afraid that the 64cc heads will give it too much compression, as there are Enginetech P1534 flat top pistons installed, so I went for the 67cc.

What is your guess on this?

Greetings Ben

I had a 260 Mercruiser (1990). Around 2015 I pulled the engine to repair a stringer. While it was out I purchased 64cc Vortec heads from Summit. I purchased Z28 valve springs about 120 lb seat pressure and only installed the outers, so no clearance issues on the Vortec heads. Inners not really required at only 5000 rpm. Installed Edelbrock Performer dual plane intake (not the RPM Air Gap), phenolic carb spacer, since I wanted to reuse the Quadrajet carb). Installed Summit 1.5 full roller rockers. Installed an exhaust tube. Installed Merc HiPo exhaust manifolds. Installed a Comp Cams hydraulic 212 / 218 @ .050 cam. Installed full roller timing chain. I think that was all I did. Used the existing Thunderbolt ignition with an MSD coil and set the timing to 30* total. Boat speed increased from 51 - 52 mph to 60 - 61 mph. Went from a 21P Mirage to a 23P Mirage and was able to turn it around 5000 rpm. Ran fine on 87 Octane but just for safety's sake, I used 89 most of the time. Idled fine, you could barely tell it had a cam in it, accelerated much better and if anything the fuel mileage was better at 28 mph cruise speed. I was very satisfied with the results.
Grusse, Glenn

Hi Glenn,

thank you for your input. That's almost the same bulid that I'm doing.

I heard lots of oppinions on my camshaft now and I think I'm good to go.

I also have my additional things together for the build:
- Summit 151124 67cc heads (not 64cc because of the compression ratio with the flat tops)
- P1534 Engintech flat top pistons are already installed
- CompCams 981-16 valve springs which match the specs of the cam (cam states 110 seat/280open, the springs have 105seat/276open)
- Edelbrock 2116 performer intake
- Chevy performance rocker arms 12495490
- Edelbrock 1409 Carb
- D.U.I. HEI marine ignition

I hope that will work out. What do you think?

What I'm afraid of is the cam break-in. I heard a lot of scary stories in the recent past of cams and lifters who fail.

Greetings
Ben

Just make sure to use proper flat tappet breakin oil, fill fuel bowls and try and set timing so she fires off right away, don’t crank engine too long, also I am super finicky and change oil right after 30 minute cam breakin, there’s tons of stuff in a fresh rebuild no matter how well you clean it first. You can’t change oil too often on fresh motor, get it to fire right away and get to 2500rpm for 20 to 30 minutes and check for leaks, good luck

I think I purchased a bottle of zinc additive from a GM dealer, and added it to the oil. Fired it up quickly, and let it run around 2500 - 3000 rpm for 15 minutes. Then I changed the oil and filter and ran it. However, with today's oils and cam and lifter quality, there is always some risk, which is one reason OEM's have switched to hydraulic roller cams. I don't remember for sure, but I think I used 20W-50 VR1 Valvoline Racing oil because it has a high zinc content for the camshaft break-in. I didn't change the bearings, rings or pistons, so I did not have to break the engine in. I also had flat top OEM pistons with 4 valve reliefs and the 64cc Vortec heads worked fine.

There is good information on Driven oil for flat tappet breakin, have a look, high zinc and low detergent for breakin